CA3127655C - Systems and methods of adaptive beamforming for mobile satellite systems based on user locations and co-channel waveforms - Google Patents
Systems and methods of adaptive beamforming for mobile satellite systems based on user locations and co-channel waveforms Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
- H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
- H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
- H04B7/0617—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal for beam forming
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- H04B7/185—Space-based or airborne stations; Stations for satellite systems
- H04B7/1853—Satellite systems for providing telephony service to a mobile station, i.e. mobile satellite service
- H04B7/18539—Arrangements for managing radio, resources, i.e. for establishing or releasing a connection
- H04B7/18541—Arrangements for managing radio, resources, i.e. for establishing or releasing a connection for handover of resources
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- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/14—Relay systems
- H04B7/15—Active relay systems
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- H04B7/216—Code division or spread-spectrum multiple access [CDMA, SSMA]
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Abstract
Description
BASED
ON USER LOCATIONS AND CO-CHANNEL WAVEFORMS
10001]
FIELD
SUMMARY
This unnecessarily compromises the beamformer's degrees of freedom to optimize the performance of each individual user. Besides, the fixed regional spot beam or sector beam is not adaptive to the users' individual operating conditions, such as: usage of power and bandwidth, and received interference power (intra-system and extra-system) as functions of time and user location. The above (and other) limitations of conventional beamforming systems are addressed in the present disclosure.
The systems and methods are applied to both the return and forward links.
(Satellite Base Station Subsystem) by the air interface.
location) may be estimated at the S-BSS from the spatial signature of return link transmissions and knowledge of the return signal waveform. Here, "spatial signature" refers to the distribution of the received power as a function of the Angle of Arrival (AoA) of the return link signal. In both embodiments, a customized, virtual beam is formed inside the S-BSS for each individual user, which maximizes the received signal-to-interference-and-noise power ratio for the particular user, considering the actual, spatial distribution of all cochannel users (i.e., the users sharing the same frequency in different beams). This customized virtual beam is referred to as a user beam, as mentioned above. The beam is referred to as "virtual" as it formed by signal processing software in the beamformer, although it performs exactly the same function as traditional, "real- beams formed by physical components such as phase shifters, amplifiers, and attenuators. Hereafter, the qualifier, "virtual," is dropped when referring to the beams of the present system.
An embodiment using frequency division duplexing (FDD) is described first.
Given explicit knowledge of the UEs' locations at the S-BSS, which may be transported from the UEs to the S-BSS via the return link as indicated above, the S-BSS can form a user beam using knowledge of the RF calibration of the satellite's antenna subsystem, or feed elements. This calibration enables the S-BSS to determine the complex weights that should be applied to each feed element in order to achieve the objective spatial signature, or transmit gain pattern, necessary to form user beams for each UE. This transmit gain pattern would be optimized to jointly maximize the gain towards the targeted (i.e. desired) UE while minimizing the gains
10008] In another embodiment, time division duplexing (TDD) using a common return and forward link frequency may be used. In this embodiment, in addition to using explicit, a priori knowledge of the UE locations to generate the beamforming weights, the S-BSS may be able to substantially reuse the weights derived from return link optimization.
maximizes the beamformer's degrees of freedom to optimize the performance of each individual user. The user beam pattern is adaptive to the user's location and the cochannel interference environment. Note that, unlike an RF or IF implementation, which is common in many traditional systems, beamforming with the user's signal bandwidth is relatively easy to implement when performed as a part of the received signal demodulation process, as it is in the embodiments presented herein.
transversal filters. Alternatively, the feed element paths may first have their frequency responses equalized over the beam's bandwidth, after which scalar multipliers can be used.
Either approach imposes a substantial burden on traditional satellite networks, especially for ground based beamforming (GBBF), compared to the requirements of the present system.
[0011a] According to an aspect of the present disclosure, there is provided a method of beamforming for a satellite system, the method comprising: during startup of the satellite system, sharing a fixed beam among a plurality of user equipment, the fixed beam formed to provide coverage for all of the plurality of user equipment in an area without regard to any individual user equipment's operating conditions; generating, with a beamformer, a customized user beam for a user equipment of the plurality of user equipment, the user equipment having a location and transmitting a pilot signal having known attributes; and subsequently transitioning from the fixed beam to the customized user beam for the user equipment.
10011b] According to another aspect of the present disclosure, there is provided an adaptive beamforming system, the system comprising: an electronic processor communicatively coupled to a satellite system and configured to during startup of the satellite system, share a fixed beam among a plurality of user equipment, the fixed beam formed to provide coverage for all of the plurality of user equipment in an area without regard to any individual user equipment's operating conditions; generate, with a beamformer, a customized user beam for a user equipment of the plurality of user equipment, the user equipment having a location and transmitting a pilot signal having known attributes; and subsequently transition from the fixed beam to the customized user beam for the user equipment.
BRIEF DESCRIPTION OF THE DRAWINGS
Date Recue/Date Received 2023-04-11
4a Date Recue/Date Received 2023-04-11
DETAILED DESCRIPTION
The disclosure is capable of other embodiments and of being practiced or of being carried out in various ways.
100331 For ease of description, the example systems or devices presented herein may be illustrated with a single exemplar of each of its component parts. Some examples may not describe or illustrate all components of the systems. Other example embodiments may include more or fewer of each of the illustrated components, may combine some components, or may include additional or alternative components.
100341 Embodiments described herein provide individual-user-optimized, adaptive beamforming for mobile satellite systems. One example system creates a 'beam for each user', referred to as 'user beam' (that is, for communication with user equipment participating in the mobile satellite system). As used herein, the term "user equipment" or "11E" includes satellite radiotelephones or data terminals, including smart telephones and access points for internet of things (loT), wherein the terminal includes a radio frequency transceiver and may also include a global positioning system (GPS) or global navigation satellite system (GNSS) receiver. The user beam is optimized based either on known user locations or the attributes, or signatures, of waveforms received from all cochannel users. The system operates in an environment of significant frequency reuse among the cochannel users. Knowledge of user locations is transferred to the S-BSS (Satellite Base Station Subsystem) by the return link or is derived at the S-BSS from estimation of the spatial signature of the return link signals with knowledge of pilot signals in the return link waveform. The user beam maximizes the signal-to-interference-noise relative to the desired user, both in the forward and return links. The optimization process considers the spatial distribution of all cochannel users in the footprint of the satellite. The user beam adapts to the user's location and co-channel interference environment. By simulation, the performance of the beamforming system is compared with an existing fixed beamforming system, represented by a major GEO MSS covering the Continental United States and Canada. The simulation results show that user-optimized adaptive beamforming offers significant capacity advantages over the legacy beamforming, measured by aggregate system throughput.
[0035] 1. New User Beamforming System and Adaptive Resource Scheduler [0036] Figure 1A illustrates a high-level block diagram of an adaptive beamforming system 100. The described methods may be applied to both cellular networks and MSS, although the present narrative treats the latter as the preferred embodiment for the purpose of explaining the concepts. Within the MSS category are included both on-board beamforming, wherein the beams are formed on the satellite, and ground based beamforming (GBBF), where the beams are formed by subsystems of a satellite earth station, or gateway. The system block diagram of Figure IA applies, in a general way, to all the above embodiments.
[0037] The following are the major elements, or subsystems, of the beamformer system 100.
[0038] Antenna array 102: A fundamental component in a beamformer is an array of multiple antennas. The antennas and their feeder electronics (which feed radio signals to and from the antenna elements) are often referred to as feed elements.
[0039] Channelizer 104: This subsystem subdivides a broad operating RF
band, for example, the MSS L-band, into sub-bands that may be more suitable as operating channel bandwidths, transmit power amplifiers, and receive low noise amplifiers.
Charmelizers are more common in satellite systems and may not be necessary in cellular systems operating with lower RF bandwidths relative to the operating frequency.
[0040] RF/1F 106: This represents analog electronics that may exist between the antenna array and the Satellite Base Station Subsystem (S-BSS). These electronics may be distributed between the satellite and the ground based gateway in satellite embodiments, or the tower head and radio access network (RAN) equipment in terrestrial cellular embodiments.
[0041] Satellite Base Station Subsystem (S-BSS) 108: This performs the RAN
functions of resource scheduling and data/signal processing required by the lower layers of the protocol stack. The following explains some differences between how beamforming is performed in existing systems and how it is performed in the embodiments discussed herein.
[0042] Traditional beamforming architecture: For transmit operation, a data stream from an upper layer of the communication protocol stack is converted into a single stream of transmit symbols. These symbols are fed to a beamformer, which may be analog or digital in implementation. The beamformer converts the single stream into M symbol-streams with appropriate relative amplitudes and phases. The said M streams are then fed to an M-element antenna array. For receive operation, the traditional beamformer linearly combines the M
received symbol streams into a single stream. The combining process applies appropriate amplitude weights and phase shifts to each stream. The said single stream is then provided to the S-BSS for receive-mode signal/data processing corresponding to the lower layers of the communications protocol stack. The above operation is performed for every beam of the network.
[0043] New Adaptive Beamformer 110: M symbol streams are passed transparently (i.e., preserving the relative amplitudes and phases of the streams, and with minimal signal distortion) to the S-BSS, as shown in Figure 1A. The example system illustrated in Figure lA includes an (in-phase and quadrature) interface for use with signals' center frequencies, which are at complex baseband. However, a bandpass IF interface may also be used without departing from the teachings of the present disclosure.
[0044] Receive Mode Operation: In the receive mode of operation, the S-BSS
receives an M-element symbol stream (i.e. a stream of complex vectors), instead of a single (i.e.
scalar) symbol stream. The linear signal processing methods described here may be used to adaptively combine the M-streams into a single stream with an improved signal-to-interference-plus-noise ratio (SINR). However, because the new architecture makes available to the S-BSS a vector of received symbols, as opposed to a post-beamformed scalar stream, which would be provided if traditional beamforming had been used, the S-BSS is able to apply powerful techniques using vector inputs, including non-linear techniques, to demodulate the symbols with greater reliability. Examples of non-linear techniques are Decision Feedback and Multiuser Detection.
[0045] Transmit Mode Operation: In the transmit mode, the S-BSS performs the function of the beamformer by producing a vector stream instead of scalar stream. The transmit vector incorporates the appropriate relative amplitude weights and phase shifts necessary to create the desired beams.
[0046] The Receive and Transmit mode beamforming operations described above are performed individually for each UE; hence the beam pattern is customized to the requirements and operating environment of each UE. It may be noted that, in traditional beamforming, it is one beam for many UEs; all UEs in a beam share the spatial attributes of that beam.
[0047] Adaptive Resource Scheduler (ARS) 112: A RAN resource scheduler is a common subsystem in existing S-BSS's but is usually very loosely coupled to the RAN. In other words, it is typically not responsive to the radio frequency characteristics of the signals received by the RAN. In the new architecture, the resource scheduler is tightly coupled to the RAN, i.e., it is an essential contributor to the adaptivity of the beamforining system. For example, the adaptive resource scheduler (ARS) determines an optimal frequency, time and power allocation for each individual user dynamically, based on the spatial distribution of all active users and their demands, which may be driven by traffic loads and Quality of Service (QOS) requirements.
[0048] Figure 1B is a block diagram of a system where the beamformer is located on the ground, which is the architecture (including both old and new embodiments) corresponding to aground-based beamformer (GBBF). In the old GBBF architecture 120, the beamformer is separate from the Satellite Base Station Subsystem (S-BSS) 108, as is the current practice, whereas in the new GBBF architecture 122, the beamforming is integrated in the S-BSS 108.
[0049] Figure 14 illustrates an example beamforming system 1400 whereby an existing, separately beamforming GBBF 1402, depicted in the old architecture of Figure 1A, can be logically bypassed in order to connect the feed element signals directly to the S-BSS. The new adaptive beamformer 1404 may be added to the existing GBBF as additional capability, while preserving the existing GBBF's traditional ability to form beams before the signals are fed to the S-BSS. Note that, in the new adaptive beamformer, the S-BSS
includes the beamforming functionality, as in current terrestrial 3GPP systems. According to the new architecture, the existing GBBF's weights are designed to transparently connect the feed element signals to the S-BSS inputs ¨ one feed element to one input. These GBBF weights comprise complex vectors where one element is set to unity (i.e., 1 + j0) and all other elements are set to zero; the weight element set to unity depends on the particular feed element that is connected to the S-BSS. The advantage of this architecture is that existing S-BSS units can continue to be served by the existing GBBF operating in its traditional modes, while the new S-BSS can access the feed elements through the existing GBBF
operating in the pass-through mode. This architecture can be applied to both return link beamfoiming and forward link beamforming.
[0050] The motivation for the bypassing of the existing GBBF, described above, may be a commercially desire to preserve the present functions of a legacy GBBF with minimal disruption, while adding the methods of the present disclosure as added beamforming options and implementing them externally (relative to the existing GBBF) in the S-BSS.
It should be obvious that, in an alternative embodiment, especially in a new implementation, the new methods may also be implemented in a standalone GBBF, with the S-BSS
performing its traditional, exclusively RAN functions. The motivation for this architectural choice may be commercial rather than technical. Because of the close coupling between elements of the RAN processing, such as the Adaptive RAN Scheduler, and beamforming, the technically optimum architecture appears to be a joint RAN Processor and Beamformer, shown as S-BSS
in Fig. 14, wherein the separate GBBF is either eliminated or bypassed, and the feed element signals are connected directly to the S-BSS.
[0051] A new concept, the "beam zone," distinct from operational spotbeams, is introduced in the new system. Beam zones are traditional, fixed (non-adaptive) spotbeams with an N-color reuse. For example, Figure 2 illustrates a plurality of beam zones 202 with the case of N = 3 shown as an example, although N may have any value. The beam zones 202 are used for frequency planning - they do not represent operational beams.
Figure 3 illustrates how the frequency and power allocation are performed by the system 100. Assume that a channel bandwidth, B, is available for the new system and, to enable 3-color frequency reuse, the band is divided into 3 segments, each having a bandwidth of 1313.
Each beam zone is allocated spectrum corresponding to one of the 3-color segments. Users located in a common beam-zone would share the same 13/3 spectrum through a multiplexing scheme such as frequency division multiplexing (FDM). Other multiplexing schemes for sharing a band among multiple users could equally be used - the use of FDM in the present disclosure should be seen as exemplary rather than essential to the core teachings about beamforming.
For example, orthogonal frequency division multiplexing, time division multiplexing, and code division multiplexing may be used. Note that, typically, the beam zones may be too small to allow separation of the users' signals via beamforming, i.e., spatial multiplexing.
This is owing to the limited aperture of the satellite's antenna array. As in traditional, fixed beam design, the beam zones are designed such that cochannel users in adjacent beam-zones have a minimum spatial isolation. Typically, the fixed beam design would incorporate pattern nulls at a number of control points in the adjacent cochannel beams.
[0052] An example frequency allocation scheme 302 is illustrated in the Figure 3. As an example of using FDM for K users inside a beam-zone, the frequency bandwidth 13/3 would be equally divided among the users with each having B/(3*K) - unequal distributions of bandwidth to users could also be used without departing from the present teachings. This implies that if there were fewer users inside the beam-zone, the user(s) could occupy more bandwidth than if there were more users inside the same beam. The additional bandwidth might be used to provide more throughput to the users to improve their Quality of Service (QOS) or, alternatively, enable the users to spread their spectrum beyond the minimum required for a targeted QOS, thereby using spread spectrum processing gain to reduce the interference to other cochannel users. As user locations and distributions change over the time, the frequency allocation dynamically adapts to the user situation accordingly.
[0053] An example resource allocation procedure 400 is summarized in the flowchart shown in Figure 4. It starts with the input definition of "beam-zone"
location, shape and size (at block 402), and frequency reuse ratio N among those "beam-zones- (at block 404), which determines the "beam-zone" layout in coverage area (at block 406). Then, based on the users' location and distribution (at block 408), the scheduler identifies users inside each -beam-zone" (at block 410). Assuming that the total available bandwidth is B
(at block 412) and that there are K users in a "beam-zone," the scheduler assigns B/(N*K) BW
for each user inside the -beam-zone" (at block 414).
[0054] In some embodiments, the users inside a "beam-zone" may use all the B/N
frequency bandwidth through '1'DMA by allocating an exclusive time slot for each of the users. In some embodiments, the users may share the B/N frequency bandwidth through combination of FDM/TDM such as in OFDMA system. In some embodiments, the users may share the B/N frequency bandwidth through CDMA, noting that if CDMA were used, a frequency reuse corresponding to N=1 may be feasible.
[0055] In distribution of the total EIRP in the forward link, in some embodiments, the adaptive resource scheduler may uniformly distribute transmit power among all active users.
This means that satellite power is distributed proportionally to users' geographic density.
[0056] Considering the return link, in some embodiments, different users may be allocated different amounts of transmit power, proportional to their QOS
needs, which may be established by a QOS negotiation with an entity in the network infrastructure (S-BSS or other entity). The unequal distribution allows different UE types to be supported in the same beam-zone.
[0057] The following applies to both forward and return link beamforming.
Once resource allocations are done, a customized beam is formed for each individual user with beam shape adaptive to cochannel UE distribution. The user beam can be formed with BF
algorithm such as adaptive minimum mean square error (MMSE) based on user locations or user reference pilot signals. The pattern generation rule includes maximizing SINR toward the desired user with consideration of the actual, spatial distribution of all cochannel users, and each user gets a custom beam. With the methods described above, the adaptive beamformer is able to optimally utilize degrees of freedom offered by the antenna feed element array. Figure 5 illustrates an example of how a user beam 500 is formed in principle under the illustrated user distribution scenario. In a conventional system, illustrated in Figure 6, a fixed regional spot beam 600 is formed for all users in the main beam 602. The fixed spot beam 600 usually minimizes total received interference plus noise (I+N), subject to specified gain constraints for main beam 602 and locations of hypothetical users in cochannel-adjacent beams 604, as illustrated in Figure 6. In contrast, as shown in Figure 5, the customized user beam 500 maximizes SINR toward the desired user, adaptive to the actual, spatial distribution of all cochannel users. The fixed beam 600 of Figure 6 would have disadvantages relative to the adaptive beam (user beam 500), such as gain degradation and adjacent cochannel beam interference for those users that are near the beam edge. The fixed beam 600 of Figure 6 also dedicates the beamformer's degrees of freedom to optimize the beam shape for hypothetical desired and undesired users, which may not represent actual user distributions or actual interference environment.
[0058] 2. Adaptive Bearufbrming Methods based on user location or waveform [0059] A customized beam is formed for each individual user with beam shape adaptive to cochannel UE distribution, informed by the ARS. The adaptive user beamfortning methods for both return link and forward link are described respectively in this section.
[0060] 2.1 Return link method [0061] Assume that a satellite (not shown) has a 2-D antenna array 702 of i'l// feed element elements (see Figure 7). The in' feed element 704 has the complex (gain and phase) response of a m(0,,, TO at azimuth angle 0, and elevation angle of p, from the satellite point of view for the km user location 706, as illustrated in Figure 7. The array steering vector at the km user location 706 is therefore defined by a(0,,,yok) = [a 109 k a2(00 gok ), = = = a m(0k,cok)1T EC ) [0062] If K user signals sk (t),k = 0,1,= = = K ¨1, arrive from (01,(p1),(02, cp,),- = = ,and (0 ) respectively, the array output vector can be expressed as a linear combination of the K incident waveforms and noise as below:
K-I
y(t)= Ea(8,,cok)s,(t)+ + n(t) k=0 (2) = A s(t) + /(t) + n(t) e curt [0063] where A = [a(0,,q),) a(), ) = = = a(0,,q), )1 (3) [0064] is the array manifold that consists of K steering vectors, and s(t) = [s, s2() = s, (t) r (4) [0065] is the vector of signal waveforms, and At) is the vector of cochannel interference that may include ancillary terrestrial component (ATC) interference, and n(l) is the additive complex Gaussian noise vector. In one embodiment, for a known location of the kth user at (8k, co, ) , to form a beam toward the kth user with the MMSE criterion, the beamformer may have the weights given by w = 11;1a(9,,cok) (5) [0066] where R = Etyyl (6) [0067] is the antenna array co-variance matrix.
[0068] In another embodiment, for a known waveform of the kth user skO, to form a beam toward the kth user with the MMSE criterion, the beamfonner may have the weights given by w = Wyir (7) ys [0069] where = Etys; (8) [0070] is the correlation vector between the received vector and reference signal, which essentially is the estimated steering vector for the kth user.
[0071] 2.2 Forward link method [0072] Forward link beamforming is different from return link beamforming because the transmit antenna elements and receive antenna elements have different feed patterns (as a function of frequency) for an FDD system such as the one in satellite. Also, unlike the return link where the received array co-variance matrix Ry can be estimated from the received array vector signal yN, the forward link array co-variance matrix obviously does not exist. In the case of the forward link, a -virtual transmit array co-variance matrix" is introduced as a part of forward link beamforming method.
[0073] As the adaptive scheduler at S-BSS has all information about the locations of all the users, and power and bandwidth allocation for all the users, a "virtual transmit array co-variance matrix" can be constructed based on this information. In some embodiments, the "virtual transmit array co-variance matrix" can be constructed based on estimated spatial steering vectors. Assume that scheduler allocates total of K cochannel users whose carrier frequency has overlaid one another, and the K cochannel user locations are at (0 ), (0 2,4) ),= = = ,and (0 ,,,q),) respectively. In addition, the corresponding allocated transmit power spectrum densities for the K cochannel users are v 1,p2, respectively.
Now let's define a cochannel transmit array co-variance matrix as the following R,. Ai.(0,T)PA,H(0, go) (9) [0074] where AT(19,V) kT('0I,V1) aT(92,4p2) === aT('O K,9K )1 (10) a1(01,1) a1(02,v2) = = = a1(0õ,y9,,) a2(01,q)1) (22(02, v2) = = = a2(0.õ,vir) EC
===
_am(Opcol) am(02õ(o2) === am (9K,co,c)_ [0075] with a m(0 gr) being the inth transmit feed element complex response at 0, and Pk p, 0 = 0 P = p 2,= = = , p,c ) p2 --= . c RKxK (11) : 0 :
0 0 = pr [0076] The matrix RT formed in Equation (9) is called as "virtual transmit array co-variance matrix". With RT being defined, the forward link beamforming weight for the /eh user at location (0,, cod is given by w = (0,, co, ) (12) [0077] where a,(0000 [al(t9k, Sok), a2(0k,q4),... m (0 k, q)k)lT E Cmxi (13) [0078] is transmit steering vector toward the desired eh user.
[0079] 2.3 Simulation Examples [0080] The performance of the new user beamforming system versus a conventional, fixed (non-adaptive), spot-beamforming system has been investigated with simulations of an L-band GEO satellite. The two systems were assumed to have the same number and spatial distribution of users. Figure 8 illustrates an example of return link (RL) beam contours produced with embodiments of the user beamforming system presented herein, while Figure 9 illustrates an example of return link (RL) beam contours with the conventional, fixed spot-beamforming system. As illustrated in Figure 8, that the user beam 802 puts a null on each cochannel user 804 while trying to maximize the gain to the desired user 806.
[0081] To quantify the performance, Monte-Carlo simulations were conducted to provide the CDF (cumulative distribution function) of Edlo+No) among all users for the two systems (adaptive and fixed). MMSE (Minimum Mean Squared Error) was the optimization criterion used for adaptive beamforming and LCMV (Linearly Constrained Minimum Variance) was the optimization criterion used for designing the fixed beams. The simulations show that the new system offers significantly better performance than the legacy system for both return link (RL) and forward link (FL), as shown in Figure 10 and Figure 11, respectively.
The improvement of user's SINR leads to improvement of the system capacity (measured as network-wide aggregate throughput). Figure 15 (chart 1500) further illustrates the performance improvements of a user beam system over a conventional fixed spot beam system.
[0082] 3. Bootstrapping of a UE in an individual-user optimized adaptive beamforming system [0083] When a UE tries to initially join the network, there is no user beam. This section presents a method to enable a UE to initially join the network and establish a user beam. We first introduce the concepts of quiescent state beams and steady state beams.
The quiescent state beams are the ones used by the S-BSS before a user beam is established to broadcast synchronization signals, reference signals, and system information (SI) that provides essential information for the UE to operate in the network. The steady state beams are the adaptively formed, individual-user-optimized beams generated by the S-BSS in the connected state. We refer to the latter as "user beams." The user beam shape adapts to the distribution of the ensemble of all cochannel UEs in the footprint of the satellite, while attempting to maximize the SNIR of the desired UE. Figure 12 illustrates the S-BSS new beam concept and definitions. The fixed regional beams 1202 are used in the quiescent state, and the user beams 1204 are used in the steady state (i.e., connected state). The fixed regional beams 1202 may initially serve the users using a traditional, 3-color frequency reuse, illustrated as an example in Figure 12. The use of a frequency reuse factor of 3 is cited as an example and is neither essential nor prescriptive. The fixed regional beam may be optimized to achieve a desired shape, such as minimum in-beam gain and minimum out-of-beam rejection at selected points in the beam's look angle, using algorithms such as the fixed LCMV. The beams could be the actual beams for a legacy system.
[0084] The bootstrap procedure for S-BSS system with adaptive user beams may be air interface dependent. Figure 13 illustrates one example embodiment of an adaptive user beam startup procedure 1300, described in terms of an LTE satellite air interface for a space-based network (SBN) 1302 and a user equipment (UE) 1304.
[0085] Step 1 - Fixed regional DL beams broadcast system information (SI), which is common to all beams, plus synchronization signals (SS) and reference signals (RS), which are unique to each of the fixed beams, as sent to the UE 1304.
[0086] Step 2¨ The UE 1304 scans all the frequency bands supported by the UE 1304, and finds the strongest beam as the beam selection candidate.
[0087] Step 3 ¨ The UE 1304 searches for SS to perform time and frequency synchronizations.
[0088] Step 4 ¨ The UE 1304 synchronizes to the SS to perform beam identification and initial frame synchronization.
[0089] Step 5 ¨ The UE 1304 performs system information (SI) acquisition on downlink physical broadcast channel (PBCH), which may include system bandwidth, PRACH
(physical random access channel) configuration information.
[0090] Step 6¨ The UE 1304 estimates the uplink timing advance by using its GPS
location information and the Satellite location information, which improves overall system latency and efficiency relative to present 3GPP methods. However, a suitable adaptation of the latter may also be used.
[0091] Step 7 ¨ The UE 1304 performs RS based reference signal received power (RSRP) measurement and send a PRACH preamble with appropriate PRACH power level to request access to the SBN 1302 with the estimated timing advance.
[0092] Step 8 ¨ A Satellite Base Station Subsystem, through the corresponding Fixed regional UL beam, detects PRACH preamble and send back random access response (RAR) which may contain UL timing command (if any timing adjustment is needed) and scheduling information pointing to radio resources that the UE 1304 can use to transmit a request to connect.
[0093] Step 9 ¨ The UE 1304 transmits a request to connect which contains its identity and location information as part of a Radio Resource Control (RRC) layer message.
[0094] Step 10¨ The SBN 1302 transmits a connection setup/resume message and contention resolution data that resolves any contention due to possible multiple UEs transmitting the same preamble in Step 7.
[0095] Step 11 ¨ The UE 1304 replies with a connection setup/resume complete message to terminate the random access procedure and complete the transition to connected state.
[0096] Step 12 - The SBN 1302 forms a user UL beam (receive beam) for the based on the UE locations or the UE reference pilot signal and network radio resource scheduling information, and switches the receive beam from the fixed UL
regional beam to the user-based UL beam for the UL data packet.
[0097] Step 13 - The SBN 1302 forms a user DL beam (transmit beam) for the based on the UE locations or the UE reference pilot and network radio resource scheduling information, and switches the transmit beam from the fixed DL regional beam to the user-based DL beam for the DL data packet.
[0098] Step 14 ¨ The SBN 1302 completes DL/UL data packet in the connected state.
[0099] Step 15 - The SBN 1302 transmits RRC connection release on PDSCH.
[00100] Step 16 - UE 1304 responds to acknowledge RRC connection release on PUSCH
RLC.
[00101] 4. Mobility Management fbr User Based Bearnfbrming Space-based Network (SBN) [00102] In idle mode, when the MME (mobile management entity) in the core network needs to page a UE, it informs the involved user beam entity in the S-BSS, so that the paging can be transmitted through the user beam. In that case, the MME has been keeping UE
history infoimation since an earlier session in the user beam. This assumes that the device is stationary since its last access to the network. However, if the device moves around when in idle mode, the MME may not have adequate information about the coverage situation changes. In this case, some level of MO (mobile originated) traffic may be used to assist the MME in keep track of the UE, and thus to improve the DL reachability for the device. For example, the network can track the device by using device-triggered location updates.
[00103] In connected mode, a UE keeps updating its location information so that the SBN
network can update the user beam weight adaptively to all cochannel user situations.
Meanwhile the SBN can determine whether the UE is still in the same "regional beam zone"
from the latest location update. If the UE is moving out of the current zone and into a neighboring "regional beam zone", the network starts the handover process by informing the UE new frequency and/or time scheduling information and updating the user beam with new beam weight accordingly since the beam weight set is dependent on the frequency allocation.
The handover to the new user beam should be seamless to the user as the user beam still maximizes SINR toward the same desired user, only adaptively to the new cochannel user situations.
[00104] In the foregoing specification, specific embodiments have been described.
However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present teachings.
[00105] Various features and advantages of some embodiments are set forth in the following claims.
Claims (58)
during startup of the satellite system, sharing a fixed beam among a plurality of user equipment, the fixed beam formed to provide coverage for all of the plurality of user equipment in an area without regard to any individual user equipment's operating conditions;
generating, with a beamformer, a customized user beam for a user equipment of the plurality of user equipment, the user equipment having a location and transmitting a pilot signal having known attributes; and subsequently transitioning from the fixed beam to the customized user beam for the user equipment.
Date Recue/Date Received 2023-04-11
Date Recue/Date Received 2023-04-11 for each of a plurality of user beams supported by the forward link, providing power to the user beam only where active user equipment is present in the user beam.
system.
Date Recue/Date Received 2023-04-11 determining, for each of a plurality of user equipment sharing a common frequency, a spatial separation; and when the spatial separation is less than a threshold value, generating a plurality of customized user beams sharing a common frequency using a multiplexing method.
while operating in an idle mode, paging the user equipment through the customized user beam to assist a mobility management entity of the satellite system in tracking the user equipment.
while operating in a connected mode, receiving, from the user equipment, an update to the location information of the user equipment; and updating a user beam weight adaptively based on the update.
determining, with a space-based network, a regional beam zone for the user equipment;
during a handoff process, determining, based on the regional beam zone, at least one selected from the group consisting of a new user equipment frequency and a time scheduling information; and updating the customized user beam with a new beam weight based on the regional beam zone.
Date Recue/Date Received 2023-04-11 transparently coupling signals to and from a satellite antenna array to a satellite base station subsystem without passing through an intermediate, separate beamformer.
an electronic processor communicatively coupled to a satellite system and configured to during startup of the satellite system, share a fixed beam among a plurality of user equipment, the fixed beam formed to provide coverage for all of the plurality of user equipment in an area without regard to any individual user equipment's operating conditions;
generate, with a beamformer, a customized user beam for a user equipment of the plurality of user equipment, the user equipment having a location and transmitting a pilot signal having known attributes; and subsequently transition from the fixed beam to the customized user beam for the user equipment.
Date Recue/Date Received 2023-04-11
generate the customized user beam by maximizing a signal to noise and interference ratio of a signal received from the user equipment.
execute the beamformer on a satellite base station subsystem, and generate a customized user beam for a return link by analyzing signals received by an antenna array carried on a satellite of the satellite system, and maximizing the signal to noise and interference ratio of the signal received from the user equipment.
for each of a plurality of user beams supported by the forward link, provide power to the user beam only where active user equipment is present in the user beam.
system.
determine, for each of a plurality of user equipment sharing a common frequency, a spatial separation; and when the spatial separation is less than a threshold value, generate a plurality of customized user beams sharing a common frequency using a multiplexing method.
while operating in an idle mode, page the user equipment through the customized user beam to assist a mobility management entity of the satellite system in tracking the user equipment.
Date Recue/Date Received 2023-04-11
while operating in a connected mode, receive, from the user equipment, an update to the location information of the user equipment; and update a user beam weight adaptively based on the update.
determine, for a space-based network, a regional beam zone for the user equipment;
during a handoff process, deterinine, based on the regional beam zone, at least one selected from the group consisting of a new user equipment frequency and a time scheduling information; and update the customized user beam with a new beam weight based on the regional beam zone.
transparently couple signals to and from a satellite antenna array to a satellite base station subsystem without passing through an intermediate, separate beamformer.
Date Recue/Date Received 2023-04-11
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WO2022155203A1 (en) * | 2021-01-13 | 2022-07-21 | Atc Technologies, Llc | Single frequency broadcasting networks using multiple spotbeams |
CN113660030A (en) * | 2021-08-18 | 2021-11-16 | 南京邮电大学 | Data transmission method for forward link of high-throughput satellite system |
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